Rolex Datejust 815143F 40 mm is the reference in this note. Use daylight if you can. Artificial light hides the difference between a faded insert and a replaced one. Hold the watch at arm length and then at reading distance. The dial should stay legible, and the hands should not disappear into the markers. On a used piece the bracelet stretches, the clasp thins at the fold, and the case back collects arcs from a desk. Those three marks are ordinary. What is not ordinary is a dial that looks new beside a bracelet that is deeply worn, or a bezel insert that is glossy beside a case that is dull. Mismatched wear means a part was swapped. Name the newer part. Then measure. Width across the bezel, lug to lug, and the space between the lugs where the strap sits. Three numbers locate the watch on a wrist better than a nickname does. Keep the nickname in your head if you like. Put the numbers and the engraving in the note.
How it differs
Rolex Datejust 815143F 40 mm is a dress case. The checks are the date window if it has one, the thinness of the lugs, and the strap or bracelet that was fitted later. A leather strap is a wearable part, not the watch. Look at the lug gap and the keeper. People change straps, hands, and crystals on dress watches. The case engraving is still the reference.
What to check on a used piece
What to check on a used Rolex Datejust 815143F 40 mm starts with the engraving. The reference to read is 815143F. Measure the case. Listings often say 40 mm, and the ruler is the check. Then check end-link play, clasp fold, and whether the hands pass each other. There is no price in this note.
Common mods
Common changes are a new strap, a replaced crown, and a crystal. The date disk, when there is one, should match the dial in color and in height. A disk that sits high or low is a note for a watchmaker, and it is still the same reference.
What people change
On the Rolex Datejust 815143F 40 mm, people change the bracelet, the case, or the movement.